Crystal detector superregenerative receiver



Dec. 18, 1951 J. C. REED, JR

CRYSTAL DETECTOR SUPERREGENERATIVE RECEIVER Filed Nov. 50, 1945 INVENTOR JOHN C. REED JR.

ATTORNEY Patented Dec. 18, 1951 CRYSTAL DETECTOR SUPERREGENERATIVE RECEIVE-R John C. Reed, .lin, Boston, Mass, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application November 30, 1945, Serial No. 531,953

4 Claims. 1

This invention relates to super-regenerative ultra-high frequency receivers, and more particularly to a super-regenerative receiver using a crystal detector.

The super-regenerative receiver is commonly used in radar beacon systems. Super regenera tion is used in order to take advantage of its great amplification, and therefore the detecting function is left for another part of the total circuit. The part which is commonly used in such circuits to perform the functions of detection is the diode.

It is generally known that diode circuits are necessarily limited in their use at the present state of the art, where frequencies in the ultrahigh frequency range are used. The primary difficulty associated with the use of diodes is relatedto the construction of the diode, which causes it to introduce reactance and resistance into associated circuits, hence lowering their Q.

The general object of the present invention is to overcome the foregoing difliculties and provide a super-regenerative receiver which operates in the ultra-high frequency range.

Another object of the present invention is to provide a super-regenerative receiver suitable for operation in the ultra-high frequency range which operates without the use of a diode tube.

A further object of the present invention is to provide a crystal in place of the usual diode tube in order to avoid the previously mentioned reactance and resistance manifestations associated with diode tubes when these are used at ultra-high frequencies.

A still further object of the present invention is to provide a crystal in place of the usual diode tube in order to avoid for the most part the distortion of any video frequency voltages which may occur at the output of the detecting circuits.

A still further object of the present invention is to provide a crystal in place of the usual diode in order to eliminate the inconvenience of filament wiring and filament power requirement Where the diode is used.

A still furthr object of the present invention is to provide a tank circuit comprising a coaxial transmission line section which is effectively an electrical length of one-half wave length.

These and other objects will be apparent from the following specification when taken with the accompanying drawing, which illustrates generally a circuit diagram of an embodiment of the invention.

In the accompanying drawing, the resonant circuit is shown as an electrical half-wave length section of concentric transmission line comprising an external conductor I! and an internal conductor 22. This line section is an open circuit at the lower end where the variable capacitor 23 varies the effective electrical length of the section. The upper end of the line section is attached to a suitable electron tube 32 having as elements a heater H, a cathode I2, a control grid l3, and plate [4.

The plate of the electron tube is directly attached to the internal conductor E2 of the coaxial line section. The plate voltage is applied to the tube at terminal 28 which leads to the plate by way of a radio frequency choke 21, and the internal conductor 22 of the coaxial line section. The function of said radio frequency choke 21 is to prevent the ultra-high frequency currents from the tank circuit from reaching the plate power source.

The grid I3 of the electron tube 32 is effectively connected for ultra-high frequency currents to the external conductor ll of the coaxial line section by the use of capacitors l5 and 29. Biasing of the grid is elfected by two methods. Cathode biasing is accomplished by resistor 3| and condenser 38. Grid leak biasing is accomplished by resistor I 6 and capacitor l5. The radio frequency choke Ill is placed in series with the cathode biasing resistor and the cathode [2 so that the cathode [2 of the electron tube may operate at radio frequency voltages above ground.

The energy from the antenna is introduced at terminal 25 which leads to a probe 24, suitably placed in the electrical field within the coaxial line section. A quench frequency source at 26 is fed into the super-regenerative amplifier. This quench-frequency source changes the grid voltage of the electron tube so that its associated resonant circuit may break into oscillation periodically in the well known manner as controlled by the quench frequency. Energy from the oscillating circuit comprising the electron tube 32 and the line section forming a resonant tank circuit, is fed into the detector circuit by means of the capacitor 2|, which comprises a conducting surface brought close to the inner conductor '22 of the coaxial line section.

The detector circuit comprises a radio frequency choke 33 which is of such reactance as tobe a high impedance to ultra-high frequency currents in the tank circuit and a low impedance to quench frequency currents, a crystal 2B which has as its function the rectification or detection of the radio frequency voltages occurring across the radio frequency choke 33, and a capacitor I!) which by-passes the ultra-high frequency components of the crystal detectors output, leaving only the fluctuating average voltages at terminal l8 which are the desired video output.

It is to be understood that the term ultra-high frequency is to carry the construction of the Federal Communications Commissions ofiicial frequency designations of March 2, 1943.

It is further to be understood that the word crystal as used in this specification is to be considered as a generic term to describe any unit of the sort which comprises for example a sharpened tungsten wire brought in contact with the surface of a silicon crystal, as distinguished from a piezo-electric crystal.

The invention described in the foregoing specification need not be limited to the details shown, which are considered to be illustrative of one form the invention may take.

What is claimed is:

1. A super-regenerative receiver for ultra-high frequency signals comprising, an electron tube including plate, cathode, and grid, a coaxial line section including internal and external conductors, said inner conductor being connected directly to said plate of said electron tube, said outer conductor being'capacitivel coupled to said control grid of said electron tube, said coaxial line section and the inner electrode capacity of said electron tube forming a resonant circuit at the frequency of said signals, a quench frequency voltage source connected to said grid to bias said electron tube to periodic non-conduction at said quench frequency for interrupting the oscillations of said tank circuit in response to said signals, a crystal detector having its input side directly capacitively coupled to the internal conductor of said coaxial line section, a choke connecting between said input side of said crystal and said external conductor, said choke having large reactance at the frequency of the oscillations of said tank and small reactance at the frequency of said quench voltage, and a capacitor connecting the output side of said crystal and said external conductor and having low reactance at the frequency of the oscillations of said tank.

2. A super-regenerative receiver for ultra-high frequency signals comprising, an electron tube including plate, cathode, and grid, a coaxial line section effectively a half-wave length in electrical length composed of an internal and an external conductor, said inner conductor being connected directly to said plate of said electron tube, said outer conductor being capacitively coupled to said control grid of said electron tube and to said cathode of said electron tube to form a resonant tank circuit at the frequency of said signals that oscillations may occur when a portion of the output at said plate is fed back in correct phase relationship to said grid, a quench frequency voltage source connected to said grid to bias said tube to periodic non-conduction at said quench frequency in order to interrupt the oscillations of the aforementioned tank circuit, such oscillations having been instigated by said signals applied thereto, a crystal detector circuit within said line capacitively coupled to the internal conductor of said coaxial resonant line section, such circuit comprising a crystal, a coupling capacitor from the input side of said crystal to the inter- .nal conductor of thecoaxial line, a radio frequency choke connected between the junction of said crystal and capacitor to the inside of the external conductor of said coaxial line section, said radio frequency choke having low reactance to said quench frequency current and high reactance to ultra-high frequency currents, a capacitor connecting the output side of said crystal to the outside of the external conductor of said line section, said capacitor having low reactance to ultra-high frequency currents emanating from said tank circuit by way of the detecting crystal.

3. A super-regenerative receiver for ultra-high frequency signals comprising, an electron tube having a cathode, an anode and a control grid, a resonator including a coaxial transmission line section coupled between grid and anode electrodes of said tube to form an oscillating circuit therewith, means for coupling said signals into said coaxial line section, a quench frequency voltage source, means applying a voltage from said source to said grid to bias said tube to pcriodic non-conduction at said quench frequency thereby to interrupt the oscillations excited in said oscillating circuit in response to said signals, a crystal detector, and means for mounting said crystal detector within the confined space be- Numb er tween the external and internal conductors of said coaxial line section in capacity coupled relationship to said internal conductor for detecting oscillations therein.

4. A super-regenerative receiver for ultra-high frequency signals comprising, an electron tube having a cathode, an anode and a control grid, a resonator including a coaxial transmission line section coupled between grid and anode electrodes of said tube to form an oscillator therewith at the frequency of said signals, a coupling loop for introducing said signals into said coaxial line section, a quench frequency voltage source, means applying a voltage from said source to said grid to bias said tube to periodic non-conduction at said quench frequency thereby to interrupt the oscillations excited in said oscillating circuit in response to said signals, a crystal detector and means for mounting said crystal detector within the confined space between the external and internal conductors of said coaxial line section in capacity coupled relationship to said internal conductor for detecting oscillations therein.

JOHN C. REED, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 2,235,010 Chaflee Mar. 18, 1941 

